I don't know that i agree. If you intend to commit a crime but due to circumstances beyond your knowladge your actions did not amount to the crime even though you intended them to, i think that is still a crime.

The question is whether there exists a nexus between the supposedly obstructing behavior and the judicial proceeding. It doesn't even matter about the intent, if there was no nexus. Can the act of having moved these materials actually impeded the course of Justice?